Natural call law is the most commonly used bridge call system. It is with 1 rank nature of design and color leaves cry, do not have by force will leave cry, 2C leaves by force call main structure frame, cooperate a few agreements to call a of composition complete call the system. The makes taste great majority to use it natural meaning that makes naturally, the content of mechanical memorizing is not much, because this compares easy study. Formulate call method naturally but Jian Kefan, not only suit bridge abecedarian, quite tall to the level card hand is likewise valuable. Accordingly, natural call law is in bridge group is very popular, get broad bridge fan greatly love.

Should see, the nature that says commonly is made is kind of call system frame only, to using means among them not only without strict regulation, and rise as what the development of the times and people know, a few content in be being made naturally also are being changed. This is caused in making this one big frame naturally, include to have various school, the nature that different area, different card hand place uses is made also not just the same. Although,these nature are made numerous brief differ, but the basic principle that does not leave natural system; Although they are difficult easy different, but all can get corresponding ideal result.

In couplet numerous play bridge, use commonly " natural " phoneticize initial " Zr " represent natural call way, commonly used natural call law has Zrnf and Zr51cf two kinds, nf ＝ " Not Force " , 1cf ＝ " 1c Force " . The distinction of law of two kinds of call depends on Zrnf and Zr51cf: 1C leaves cry, be not to force in Zrnf call law cry, and be to force in Zr51cf cry. Bishop of group of the nation before Zrnf call law can be used drills Zhang Desheng is couplet numerous write " law of call of nature of couplet numerous standard " . Zr51cf criterion version of neither one standard, zr51cf of temporarily OK and referenced fast gunman and Zr51cf of net I husband.

In bridge base online (BBO) play bridge, the yellow card of standard United States that current natural call law is OKBridge simplifies edition (SA-YC OKBridge-style Simplified) .